Method of making a non-compliant balloon for a catheter

ABSTRACT

An intravascular catheter system for properly implanting a stent in a body lumen generally comprising a catheter having an elongated shaft with an inflatable balloon formed of compliant material and a stent mounted on the working length of the balloon. The balloon material is compliant within the working range of the balloon to provide substantial radial expansion. The wingless radially expansive balloon expands in a uniform manner, thereby producing uniform expansion and implantation of the stent. Another embodiment is directed to a balloon catheter, having a semi-compliant balloon or a noncompliant balloon formed at least in part of a block copolymer.

This application is a divisional of application Ser. No. 09/733,120filed Dec. 8, 2000 now abandoned which is continuation-in-partapplication of Ser. No. 09/295,694, filed Apr. 21, 1999, now U.S. Pat.No. 6,488,688 which is a continuation-in-part application of Ser. No.09/063,969, filed Apr. 21, 1998, now U.S. Pat. No. 6,287314.

BACKGROUND OF THE INVENTION

The invention relates to the field of intravascular catheters, and moreparticularly to a balloon catheter.

In percutaneous transluminal coronary angioplasty (PTCA) procedures aguiding catheter is advanced until the distal tip of the guidingcatheter is seated in the ostium of a desired coronary artery. Aguidewire, positioned within an inner lumen of an dilatation catheter,is first advanced out of the distal end of the guiding catheter into thepatient's coronary artery until the distal end of the guidewire crossesa lesion to be dilated. Then the dilatation catheter, having aninflatable balloon on the distal portion thereof, is advanced into thepatient's coronary anatomy over the previously introduced guidewireuntil the balloon of the dilatation catheter is properly positionedacross the lesion. Once properly positioned, the dilatation balloon isinflated with liquid one or more times to a predetermined size atrelatively high pressures (e.g. greater than 8 atmospheres) so that thestenosis is compressed against the arterial wall and the wall expandedto open up the passageway. Generally, the inflated diameter of theballoon is approximately the same diameter as the native diameter of thebody lumen being dilated so as to complete the dilatation but notoverexpand the artery wall. Substantial, uncontrolled expansion of theballoon against the vessel wall can cause trauma to the vessel wall.After the balloon is finally deflated, blood flow resumes through thedilated artery and the dilatation catheter can be removed therefrom.

In such angioplasty procedures, there may be restenosis of the artery,i.e. reformation of the arterial blockage, which necessitates eitheranother angioplasty procedure, or some other method of repairing orstrengthening the dilated area. To reduce the restenosis rate and tostrengthen the dilated area, physicians frequently implant anintravascular prosthesis, generally called a stent, inside the artery atthe site of the lesion. Stents may also be used to repair vessels havingan intimal flap or dissection or to generally strengthen a weakenedsection of a vessel. Stents are usually delivered to a desired locationwithin a coronary artery in a contracted condition on a balloon of acatheter which is similar in many respects to a balloon angioplastycatheter, and expanded to a larger diameter by expansion of the balloon.The balloon is deflated to remove the catheter and the stent left inplace within the artery at the site of the dilated lesion. See forexample, U.S. Pat. No. 5,507,768 (Lau et al.) and U.S. Pat. No.5,458,615 (Klemm et al.), which are incorporated herein by reference.Thus, stents are used to open a stenosed vessel, and strengthen thedilated area by remaining inside the vessel.

In conventional stent deploying balloon catheters, the balloon is madeof essentially non-compliant material, such as nylon orpolyethyleneterephthalate (PET). Such non-compliant material exhibitslittle expansion in response to increasing levels of inflation pressure.Because the non-compliant material has a limited ability to expand, theuninflated balloon must be made sufficiently large that, when inflated,the balloon has sufficient working diameter to compress the stenosis andopen the patient's passageway. However, a large profilenon-compliantballoon can make the catheter difficult to advance through the patient'snarrow vasculature because, in a uninflated condition, such balloonsform flat or pancake shape wings which extend radially outward.Consequently, the wings of an uninflated balloon are typically foldedinto a low profile configuration for introduction and advancementthrough the vessel. The wings are again produced upon deflation of theballoon following stent deployment within the patient. These wings onthe deflated balloon are undesirable because they result in an increasedballoon profile which can complicate withdrawing the catheter afterstent deployment.

Although stents have been used effectively for some time, theeffectiveness of a stent can be diminished if it is not properlyimplanted within the vessel. For example, expansion of a balloon foldedinto a low profile configuration for introduction into the patient, cancause nonuniform expansion of a stent mounted on the balloon. Thenonuniform expansion of conventional designs has resulted in the use ofan elastic sleeve around the balloon and under the stent to distributeforce from the expanding folded balloon to the stent uniformly, see forexample U.S. Pat. No. 5,409,495 (Osborn), which is incorporated hereinby reference. However, such sleeves may fail to completely prevent thenonuniform expansion of the stent, they increase the deflated profileupon insertion into the patient, and they complicate the assembly of thestent onto the balloon. Additionally, the final location of theimplanted stent in the body lumen may be beyond the physician's controlwhere longitudinal growth of the stent deploying balloon causes thestent's position on the balloon to shift during deployment. As theballoon's axial length grows during inflation, the stent may shiftposition along the length of the balloon, and the stent may be implantedupstream or downstream of the desired location in the body lumen. Thus,balloons which have a large amount of longitudinal growth duringinflation provide inadequate control over the location of the implantedstent.

Therefore, what has been needed is an improved catheter balloon. Thepresent invention satisfies these and other needs.

SUMMARY OF THE INVENTION

The invention is directed to a catheter balloon having improvedperformance due to a desired degree of balloon compliance The termcompliance as used herein should be understood to refer to the radialcompliance of the balloon unless otherwise stated. One embodiment of theinvention is directed to a stent delivery system with a stent deployingballoon formed of compliant material that uniformly expands the stent toproperly implant the stent within the patient's body lumen. Anotherembodiment is directed to a balloon catheter having a balloon exhibitingsemi-compliance or noncompliance, and a method of making the balloon.

The stent delivery system of the invention generally comprises acatheter having an elongated shaft with an inflatable balloon on adistal portion of the catheter and a stent disposed about the workinglength of the balloon. The balloon is formed of material compliant atleast within a working range of the balloon, and which thereforeprovides for substantially uniform radial expansion within the workingrange. The compliant balloon material therefore expands substantiallyelastically when pressurized at least within the pressure rangedisclosed herein for use in inflating the stent deploying balloon of theinvention. The compliant balloon material will generally be an highlyelastic material. The term “compliant” as used herein refers tothermosetting and thermoplastic polymers which exhibit substantialstretching upon the application of tensile force. Additionally,compliant balloons transmit a greater portion of applied pressure beforerupturing than non-compliant balloons. Suitable compliant balloonmaterials include, but are not limited to, elastomeric materials, suchas elastomeric varieties of latex, silicone, polyurethane, polyolefinelastomers, such as polyethylene, flexible polyvinyl chloride (PVC),ethylene vinyl acetate (EVA), ethylene methylacrylate (EMA), ethyleneethylacrylate (EEA), styrene butadiene styrene (SBS), and ethylenepropylene diene rubber (EPDM). The presently preferred compliantmaterial has an elongation at failure at room temperature of at leastabout 250% to at least about 500%, preferably about 300% to about 400%,and a Shore durometer of about 50A to about 75D, preferably about 60A toabout 65D.

When the stent delivery balloon of the invention is pressurized, theballoon expands radially in a uniform manner to a working diameter.Because the balloon expands uniformly without unwrapping wings, it willuniformly expand a stent mounted on the balloon. The uninflated balloondoes not require folding into a low profile configuration for insertioninto the patient or the use of elastomeric sleeves used withconventional stent deploying balloons made from relatively non-compliantmaterial. Similarly, the balloon of the invention should have asubstantial elastic recoil so that it deflates into a smaller diameterwith little or no wings. The undesirable flat or pancake shape wingswhich form when conventional stent deploying balloons are deflated arethus avoided. Additionally, minimal axial growth of the balloons duringinflation provides improved control over the placement of the implantedstent in the body lumen. The compliant balloon results in improvedabrasion and puncture resistance relative to the conventionalnon-compliant stent deploying balloons at least in part because there islittle or no movement between the balloon and stent when the balloonexpands radially. Moreover, due to the compliant nature of the balloon,there is a more highly efficient transfer of force to the stent thanwith the high pressure non-compliant conventional balloons which expendmuch expansive force to overcome rigidity (non-compliance) and to sizethe stent.

In another embodiment, the balloon catheter having a semi-compliantballoon generally comprises a catheter having an elongated shaft with aninflatable balloon on a distal portion of the shaft. The semi-compliantballoon is formed at least in part of a block copolymer, such as apolyurethane block copolymer. The term semi-compliant should beunderstood to mean a balloon with low compliance, which thereforeexhibits moderate stretching upon the application of tensile force. Thesemi-compliant balloon has a compliance of less than about 0.045millimeters/atmospheres (mm/atm), to about rupture, in contrast tocompliant balloons such as polyethylene balloons which typically have acompliance of greater than 0.045 mm/atm. The percent radial expansion ofthe balloon, i.e., the growth in the balloon outer diameter divided bythe nominal balloon outer diameter, at an inflation pressure of about150 psi (10.2 atm) is less than about 4%. Another embodiment of theinvention comprises a noncompliant balloon, preferably formed at leastin part of a polyurethane block copolymer, which has a compliance of notgreater than about 0.025 mm/atm.

In a presently preferred embodiment, the semi-compliant or noncompliantballoon is formed of a polyurethane block copolymer. Suitablepolyurethane block copolymers include polyether based polyurethanes suchas PELLETHANE available from Dow Plastics, polyester based polyurethanessuch as PELLETHANE available from Dow Plastics and ESTANE available fromBF Goodrich, polyether based aromatic polyurethanes such as TECOTHANEavailable from Thermedics, polyether based aliphatic polyurethanes suchas TECOPHILIC available from Thermedics, polycarbonate based aliphaticpolyurethanes such as CARBOTHANE available from Thermedics,polycarbonate based aromatic polyurethanes such as BIONATE availablefrom The Polymer Technology Group (PTG), solution grade polyurethaneurea such as BIOSPAN available from PTG, and polycarbonate-siliconearomatic polyurethane such as CHRONOFLEX available from Cardiotech.Other suitable block copolymers may be used including TEXIN TPUavailable from Bayer, TECOPLAST available from Thermedics, and ISOPLASTavailable from Dow.

One aspect of the invention is directed to a catheter balloon which isaxially noncompliant. The terminology “axially noncompliant” should beunderstood to mean a balloon having a length which exhibits little or noaxial growth during inflation of the balloon. The axially noncompliantballoon has an axial compliance of less than about 0.25 mm/atm, to aboutrupture. The length of the balloon increases by less than about 2.5% toabout 20% over an inflation pressure range of about 60 psi (4 atm) toabout 315 psi (21 atm), and by less than about 5% to about 15% within aninflation pressure range of about 90 psi (6 atm) to about 205, psi (14atm). The balloon therefore avoids the trauma to the vessel wall causedwhen ends of an axially elongated balloon expand against a portion ofthe vessel wall. The invention also includes a method of making asemi-compliant balloon. The method generally comprises extruding atubular product formed at least in part of a block copolymer, such as apolyurethane block copolymer. The extruded tubular product is heated toa first elevated temperature and the outer diameter of the tubularproduct is expanded to a second outer diameter. While still underpressure, the expanded tubular product is heated at a second elevatedtemperature. The second elevated temperature is equal to or greater thanthe first elevated temperature. The expanded, heat-treated tubularproduct is then cooled to form the semi-compliant balloon. The tubularproduct is preferably heated to the first and second elevatedtemperatures by locally heating the tubular member with a heating memberdisplaced along a length of the tubular product. The resulting balloonsare semi-compliant, and axially noncompliant with low axial growthduring inflation. The invention also includes a method of making anoncompliant balloon.

The semi-compliant block copolymer balloon of the invention providesimproved performance due to the strength and softness of the balloon,with controlled expansion at relatively high pressures, and without thestiffness or poor refold characteristics of noncompliant balloons.Moreover, the low axial growth of the balloon during inflation providesimproved control over the dilatation of a stenosis or implantation of astent.

These and other advantages of the invention will become more apparentfrom the following detailed description of the invention and theaccompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view partially in section of a catheter systemwhich embodies features of the invention, showing the balloon and stentin an unexpanded state.

FIG. 2 is a transverse cross sectional view of the catheter system ofFIG. 1 taken along lines 2-2.

FIG. 3 is a transverse cross sectional view of the catheter system ofFIG. 1 taken along lines 3-3.

FIG. 4 is an elevational view partially in section of the distal sectionof the catheter system of the invention as shown in FIG. 1 depicting theballoon and stent expanded.

FIG. 5 is a transverse cross sectional view of the expanded balloon andstent of FIG. 4 taken along lines 5-5.

FIG. 6 illustrates the catheter system shown in FIG. 1, depicting theballoon in a deflated state and the stent implanted within the patient'slumen.

FIG. 7 illustrates a balloon catheter having a semi-compliant balloonwhich embodies features of the invention.

FIG. 8 illustrates a transverse cross section of the balloon cathetershown in FIG. 7, taken along lines 8-8.

FIG. 9 illustrates a transverse cross section of the balloon cathetershown in FIG. 7, taken along lines 9-9.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an intravascular catheter system which embodiesfeatures of the invention for implanting a stent in a body lumen. Thecatheter system of the invention generally includes a catheter 10 havingan elongated catheter shaft 11 having a proximal 12 and distal 13section, a radially expansive inflatable balloon 14 on the distalsection 13 of the catheter shaft 11, a stent 16 mounted on the balloon14, and an adapter 17 mounted on the proximal section 12 of shaft 11.

In FIG. 1, the catheter system is illustrated within a patient's bodylumen 18, with the stent 16 in an unexpanded state prior to expansion ofthe balloon 14. The inflatable balloon 14 is formed of radiallyexpansive material that is compliant within the working range of theballoon. As best illustrated in FIG. 3, the compliant balloon isessentially wingless and does not require folding into a low profileconfiguration for insertion into the patient. FIG. 4 illustrates theballoon in an expanded state during stent deployment. FIG. 5 illustratesa transverse cross section of the balloon illustrated in FIG. 4 takenalong lines 5-5.

In the embodiment illustrated in FIG. 1, the catheter shaft 11 has anouter tubular member 19 and an inner tubular member 20 disposed withinthe outer tubular member and defining, with the outer tubular member,inflation lumen 21. Inflation lumen 21 is in fluid communication withthe interior chamber 15 of the inflatable balloon 14. The inner tubularmember 20 has an inner lumen 22 extending therein which is configured toslidably receive a guidewire 23 suitable for advancement through apatient's coronary arteries. The distal extremity of the inflatableballoon 14 is sealingly secured to the distal extremity of the innertubular member 20 and the proximal extremity of the balloon is sealinglysecured to the distal extremity of the outer tubular member 19.

The balloon 14 may be formed of any compliant material, and includesthermoplastic and thermosetting polymers. The presently preferredcompliant polymeric materials providing a wingless balloon withsubstantially elastic recoil during deflation include polyurethanes suchas TECOTHANE from Thermedics. TECOTHANE is a thermoplastic, aromatic,polyether polyurethane synthesized from methylene diisocyanate (MDI),polytetramethylene ether glycol (PTMEG) and 1,4 butanediol chainextender. TECOTHANE grade 1065D is presently preferred, and has a Shoredurometer of 65D, an elongation at break of about 300%, and a hightensile strength at yield of about 10,000 psi. However, other suitablegrades may be used, including TECOTHANE 1075D, having a Shore D of 75.Balloons produced from the TECOTHANE materials are particularlypreferred because the axial growth of the balloon during inflation inminimized, and the axial and radial size of the balloon deflates to theoriginal preinflation size following inflation and deflation of theballoon. Thus, inflation produces little or no axial or radial growth,so that the deflated balloons elastically recoil to the preinflationsize. Other suitable compliant polymeric materials which deflate so thatat least the radial size of the balloon returns to the originalpreinflation radial size, and which therefore have a substantiallyelastic recoil after deflation, include ENGAGE from DuPont DowElastomers (an ethylene alpha-olefin polymer) and EXACT, available fromExxon Chemical, both of which are thermoplastic polymers and arebelieved to be polyolefin elastomers produced from metallocenecatalysts. Other suitable compliant materials include, but are notlimited to, elastomeric silicones, latexes, and urethanes. The type ofcompliant material may be chosen to provide compatibility with thecatheter shaft material, to thereby facilitate bonding of the balloon tothe catheter.

The stent deploying balloon of the invention can be produced byconventional techniques for producing catheter inflatable members, andmay be preformed by stretching a straight tube formed of the compliantmaterial or formed in situ after attachment to the catheter shaft.Because the compliant material provides substantial radial expansion,the balloon need not be preformed, unlike non-compliant stent deployingballoons, so that production of the compliant balloon catheter of theinvention is simplified relative to conventional non-compliant ballooncatheters.

FIG. 2, showing a transverse cross section of the catheter shaft 11,illustrates the guidewire receiving lumen 22 and inflation lumen 21. Theballoon 14 can be inflated by radiopaque fluid from an inflation port24, from inflation lumen 21 contained in the catheter shaft 11, or byother means, such as from a passageway formed between the outside of thecatheter shaft and the member forming the balloon, depending on theparticular design of the catheter. The details and mechanics of ballooninflation vary according to-the specific design of the catheter, and arewell known in the art.

The compliant balloon has sufficient strength to withstand the inflationpressures needed to inflate the balloon and expand the stent mountedthereon. The burst pressure of the compliant balloon (about 3.0 mm) isabout 10 atm to about 15 atm, and the tensile strength of an AmericanStandard Testing Method (ASTM) “dog-bone” sample cut from a compressionmolded sheet of material is about 3000 psi to about 7500 psi. The hoopstrength, e.g. the product of the burst pressure and the balloondiameter, divided by two times the balloon wall thickness, of a 3.0 mmballoon of the invention is about 10,000 psi to about 20,000 psi. Thehoop strength of a 2.5 mm balloon formed from TECOTHANE 1065D is about18,000 psi. The inflation pressure needed to expand a stent variesdepending on the balloon material and stent material and design, but isgenerally about 6 atm to about 8 atm.

The compliant material may be cross linked or uncrosslinked, dependingupon the balloon material and characteristics required for a particularapplication. The presently preferred polyurethane balloon materials arenot crosslinked. However, other suitable materials, such as thepolyolefinic polymers ENGAGE and EXACT, are preferably crosslinked. Bycrosslinking the balloon compliant material, the final inflated balloonsize can be controlled. Conventional crosslinking techniques can be usedincluding thermal treatment and E-beam exposure. After crosslinking,initial pressurization, expansion, and preshrinking, the balloon willthereafter expand in a controlled manner to a reproducible diameter inresponse to a given inflation pressure, and thereby avoid overexpandingthe stent to an undesirably large diameter.

The catheter shaft will generally have the dimensions of conventionaldilatation or stent deploying catheters. The length of the catheter 10may be about 90 cm to about 150 cm, and is typically about 135 cm. Theouter tubular member 19 has a length of about 25 cm to about 40 cm, anouter diameter (OD) of about 0.039 in to about 0.042 in, and an innerdiameter (ID) of about 0.032 in. The inner tubular member 20 has alength of about 25 cm to about 40 cm, an OD of about 0.024 in and an IDof about 0.018 in. The inner and outer tubular members may taper in thedistal section to a smaller OD or ID.

The length of the compliant balloon 14 may be about 1 cm to about 4 cm,preferably about 1.5 cm to about 3.0 cm, and is typically about 2.0 cm.In an uninflated or deflated state the balloon diameter is generallyabout 0.015 in (0.4 mm) to about 8 in (2 mm), and is typically about0.037 in (1 mm), and the wall thickness is generally about 0.004 in (0.1mm) to about 0.016 in (0.4 mm), and is typically about 0.008 in (0.2mm). In an expanded state, the balloon diameter is generally about 0.06in (1.5 mm) to about 0.18 in (4.5 mm), and the wall thickness is about0.0005 in (0.012 mm) to about 0.0025 in (0.06 mm).

Various designs for dilatation catheters well known in the art may beused in the catheter system of the invention. For example, conventionalover-the-wire dilatation catheters for angioplasty usually include aguidewire receiving lumen extending the length of the catheter shaftfrom a guidewire port in, the proximal end of the shaft. Rapid exchangedilatation catheters generally include a short guidewire lumen extendingto the distal end of the shaft from a guidewire port located distal tothe proximal end of the shaft.

When delivering a stent into a patient, the catheter 10 is inserted intoa patient's vasculature to the desired location which is shown in FIGS.1 and 4 as a dilated stenotic region, and inflation fluid is deliveredthrough the inflation lumen 21 to the compliant balloon 14 through theinflation port 24. Because of the balloon's compliant material, itexpands radially. Longitudinal growth can be prevented by the innertubular member 20 or by stretching or axial orientation duringprocessing. Consequently, the stent 16 mounted on the balloon expandsuniformly. When the inflation fluid is removed, the balloon 14 retractsto a wingless shape from elastic recoil to allow the catheter to bewithdrawn. The stent remains in place in the patient's body lumen, asillustrated in FIG. 6, showing the deflated balloon 14 and expandedstent 16 within the body lumen 18. The stent 16 may be any of a varietyof stent materials and forms designed to be implanted by an expandingmember, see for example U.S. Pat. No. 5,514,154 (Lau et al.) and U.S.Pat. No. 5,443,500 (Sigwart), incorporated by reference. For example,the stent material may be stainless steel, a NiTi alloy, a Co—Cr—Mocontaining alloy such as MP-35N, a plastic material, or various othermaterials. The stent has a smaller diameter for insertion andadvancement into the patient's lumen which may be formed by contractingthe stent or by folding at least a portion of the stent into a wrappedconfiguration.

EXAMPLE 1

TECOTHANE 1065D was used to prepare balloon tubing having a mean ID ofabout 0.0195 inch (0.5 mm) and a mean OD of about 0.0355 inch (0.9 mm),and the balloon tubing was used to prepared balloons having an OD ofabout 2.5 mm. The mean balloon OD was about 0.110 inch (2.8 mm), andmean dual wall thickness was about 0.0015 inch (0.038 mm). The meanrupture pressure was about 238 psi, and the mean hoop strength was about18,000 psi. Radial (OD) and axial (length) compliance measurements weremade on the unrestrained balloons. The term unrestrained refers to aballoon with one end attached to an inflation medium source and theother end clamped shut, as opposed to a balloon with proximal and distalends secured to a catheter shaft. The balloons have a substantiallyuniform radial expansion, as illustrated in Table 1, which lists theaverage balloon OD for the unruptured balloons, at a given inflationpressure, for five balloons tested. The balloons also have minimal axialgrowth during inflation, as illustrated in Table 2, which lists theaverage working length for the unruptured balloons, of five balloonstested, at a given inflation pressure. The axial growth, to rupture, ofthe balloons is about 32% to about 35% of the original, uninflated 20 mmworking length. Moreover, this axial lengthening would be expected to beless in a secured balloon having proximal and distal ends secured to acatheter shaft.

TABLE 1 Inflation Pressure Average Balloon (PSI) OD (MM) 30 2.476 452.743 60 2.917 75 3.044 90 3.148 105 3.239 120 3.324 135 3.405 150 3.482165 3.560 180 3.634 195 3.709 210 3.776 225 3.853 240 3.996 255 4.089

TABLE 2 Inflation Pressure Average Balloon (PSI) Working Length (MM) 3020.6 45 21.4 60 22.4 75 22.8 90 23.6 105 24.1 120 24.5 135 24.9 150 25.4165 25.6 180 26.1 195 26.5 210 26.5 225 26.75 240 27 255 27

FIG. 7 illustrates another embodiment of the invention generallyComprising a balloon catheter having a balloon which exhibits notgreater than semi-compliant expansion. The balloon catheter 100 issimilar in many respects to the balloon catheter 10 illustrated in FIG.1, with similar components being identified with the same referencenumerals. In one embodiment, the balloon catheter has a semi-compliantballoon. The catheter generally includes an elongated shaft 11 having aproximal section 12, a distal section 13, a semi-compliant balloon 114,and an adapter 17 mounted on the proximal section of the shaft. Thecatheter includes an outer tubular member 19, inner tubular member 20,inflation lumen 21, and guidewire lumen 22, as outlined above. In apresently preferred embodiment, the balloon 114 typically forms wings,which may be folded into a low profile configuration (not shown) forintroduction into and advancement within the patient's vasculature.FIGS. 8 and 9 illustrate transverse cross sections of the ballooncatheter shown in FIG. 7, taken along lines 8-8 and 9-9, respectively.To the extent not discussed herein, the dimensions and uses of thecatheter 100 having a semi-compliant balloon 114 are similar to thosedescribed for catheter 10.

In one embodiment of the invention, the balloon 114 exhibitssemi-compliant expansion. The semi-compliant balloon 114 expands amoderate amount, less than a compliant balloon but more than anoncompliant balloon, in response to increasing inflation pressure. Thesemi-compliant balloon 114 preferably exhibits not less thansemi-compliant expansion, so that the balloon preferably has acompliance of not less than 0.025 mm/atm over the desired inflationpressure range. The balloon 114 has a compliance of less than about0.045 mm/atm, and preferably from about 0.025 to about 0.04 mm/atm, overan inflation pressure range of about 30-90 psi (2-6 atm) to about 285psi (19.4 atm). The percent radial expansion is less than about 4%, andpreferably from about 1.5% to about 4%, at an inflation pressure ofabout 150 psi (10.2 atm).

The semi-compliant balloon 114 is formed from a block copolymer. In apresently preferred embodiment, the block copolymer is a polyurethaneblock copolymer. The Shore durometer hardness of the block copolymer isabout 80A to about 82D, preferably about 55D to about 75D. The flexuralmodulus of the block copolymer is about 10,000 to about 370,000 psi,preferably about 150,000 to about 300,000 psi. One presently preferredpolyurethane is PELLETHANE grade 2363, which is an ether basedpolyurethane elastomer having a Shore durometer hardness of 75D.However, other suitable grades may be used, including but not limited toPELLETHANE 2363 having a Shore durometer hardness of 55D or 65D may alsobe used. PELLETHANE 2363 is a polytetramethylene glycol basedpolyurethane, synthesized from aromatic diisocyanate and short chaindiol chain extenders such as butanediol. In a presently preferredembodiment, the rupture pressure of the balloon is about 265 psi toabout 450 psi. The working range, or pressure at which the balloon istypically inflated within the body, is about 90 psi to about 285 psi.

The balloon embodying features of the invention is axially noncompliant,and exhibits minimal axial growth as the pressure is increased duringinflation. The balloon has low axial growth of less than about 5% toabout 20% over the working range of the balloon (about 90 psi to about285 psi), and an axial compliance of about 0.1 mm/atm to about 0.25mm/atm within an inflation pressure range of about 90 psi to about 205psi. The length of the balloon increases by less than about 5% to about10% at an inflation pressure of about 150 psi (10.2 atm).

The semi-compliant balloon 114 of the invention is made according to amethod of the invention. In a method of making a semi-compliant balloon,balloon tubing comprising a block copolymer extruded into a tubularproduct is radially expanded to form the balloon by heating the tubularproduct at a first elevated temperature and subjecting the tubularproduct to an expansion pressure. The balloon is typically formed withina mold having dimensions close to the dimensions of the desired balloon.The blow up ratio, i.e., the balloon outer diameter divided by theballoon tubing inner diameter, is typically about 5.0 to about 8.0, andpreferably about 7.0 to about 8.0. The tubular product may also beaxially elongated by stretching before, during, or after being radiallyexpanded. In a presently preferred embodiment, to heat the tubularproduct to the first elevated temperature during the radial expansion, aheating member such as a heat nozzle is displaced along a length of thetubular product within the mold, to thereby apply heat to portions ofthe tubular product adjacent to the heating member. The expanded tubularproduct is then heat treated at a second elevated temperature which isequal to or greater than the first elevated temperature, by displacingthe heating member along a length of the tubular product from one end ofthe balloon to the other end. The first temperature is about 80° C. toabout 120° C., and preferably about 95° C. to about 105° C. The secondtemperature is about 100° C. to about 140° C., and preferably about 110°C. to about 140° C. (measured in mold temperature). In a presentlypreferred embodiment, the second temperature is greater than the firsttemperature. The second temperature is typically no more than about 10°C. to about 50° C., preferably no more than about 10° C. to about 20°C., greater than the first temperature. In one embodiment, a balloonhaving a 3.0 mm nominal outer diameter heat treated at a second elevatedtemperature equal to or above the first elevated temperature and havinga blow up ratio of about 7 to about 8, inflates to the 3.0 mm outerdiameter at about 6 atm to about 7 atm, and has a ¼ outer diameter sizeincrease at about 13 atm to about 14 atm for a blow up ratio of about 7,and about 18 atm to about 20 atm for a blow up ratio of about 8. Theheating member is typically displaced at a rate that is less than therate at which heating member was displaced during the expansion of thetubular product. The balloon is then cooled within the mold underpressure.

Semi-compliant balloons were prepared according to the method of theinvention, as set forth in the following examples.

EXAMPLE 2

Balloons having a nominal OD of about 3.0 mm, and a length of about 20mm were prepared using the method of the invention. PELLETHANE 75D wasused to prepare balloon tubing having an ID of about 0.015 inch (0.381mm) to about 0.0195 inch (0.495 mm), and an OD of about 0.031 inch(0.787 mm) to about 0.036 inch (914 mm). The balloon tubing was heatedand stabilized at 40° C. for 16 to 24 hours prior to being blown intoballoons. The balloon tubing was then placed in a balloon mold andstretched axially, and the mold was heated to a wall temperature ofabout 100-120° C. To expand the balloon tubing, the tubing was heated toa blow temperature of about 100° C., by displacing a heat nozzle atabout 1 mm/sec to about 5 mm/sec from one end of the mold to theopposite end, while pressurizing the tubing at an expansion pressure ofabout 220 psi to about 270 psi. The expanded tubing was then heattreated within the mold and at the expansion pressure, at a heattreating temperature equal to, or about 10° C. to about 20° C. greaterthan the blow temperature by displacing the heat nozzle from one end ofthe mold to the opposite end at a slower speed than the speed usedduring the blowing, of about 1.0 mm/sec to about 2.0 mm/sec. Thepressurized balloon was then cooled to room temperature within the mold.The resulting balloons had a percent radial expansion of about 1.5 toabout 4.0%, an elastic stress response, i.e., growth in balloon OD atabout 5 atm after inflation to about 10 atm divided by the initialballoon OD at about 5 atm, of about 0.25%, and a wall tensile strengthof about 15,000 to about 16,000 psi.

EXAMPLE 3

PELLETHANE 75D was used to prepare balloon tubing having an ID of about0.017 inch (0.43 mm) and an OD of about 0.032 inch (0.8 mm), and theballoon tubing was used to prepared a balloon having a nominal OD ofabout 3.0 mm using the method of the invention as outlined above, inwhich the expanded tubing was heat treated at a temperature greater thanthe blowing temperature. The rupture pressure was about 300 psi to about350 psi. Radial (OD) and axial (length) compliance measurements weremade on the unrestrained balloon. The term “unrestrained” refers to aballoon with one end attached to an inflation medium source and theother end clamped shut, as opposed to a balloon with proximal and distalends secured to a catheter shaft. The balloon has a semi-compliantradial expansion, as illustrated in Table 3, which lists the balloon ODfor the unruptured balloon, at a given inflation pressure. Thecompliance of the balloon over a pressure range of about 30 psi to about300 , or to about the rupture pressure, is 0.037 mm/atm. The balloonalso has minimal axial growth during inflation, as illustrated in Table4, which lists the working length for the unruptured balloons at a giveninflation pressure. The axial growth, to rupture, of the balloons isabout 25% of the original, uninflated 20 mm working length. Moreover,this axial lengthening would be expected to be less in a secured balloonhaving proximal and distal ends secured to a catheter shaft.

TABLE 3 Inflation Pressure (PSI) Balloon OD (MM) 30 2.674 45 2.757 602.835 75 2.901 90 2.951 105 2.995 120 3.034 135 3.068 150 3.099 1653.127 180 3.155 195 3.183 210 3.208 225 3.231 240 3.257 255 3.279 2703.302 285 3.326 300 3.35

TABLE 4 Inflation Pressure Balloon Working Length (PSI) (MM) 30 20.5 4520.5 60 21 75 21 90 21.5 105 21.5 120 22 135 22 150 22.5 165 22.5 180 23195 23 210 23 225 23.5 240 24 255 24 270 24 285 24.5 300 25

In another embodiment, the balloon catheter 100 has a noncompliantballoon 114 formed of a block copolymer. The noncompliant balloon issimilar in many respects to the semi-compliant balloon but with acompliance of about 0.025 mm/atm or less over the working range of theballoon, or about 8% to about 12% of the 3.0 mm outer diameter of a 3.0mm outer diameter balloon, over a working pressure range of about 7 atmto about 20 atm of the balloon (i.e., the growth in the balloon outerdiameter divided by 3.0 mm). The noncompliant balloon is made accordingto a method similar to the method used to make the semi-compliantballoon. In one embodiment, the blow up ratio of the balloon greaterthan about 8. Generally, the blow up ratio used in preparing thenoncompliant balloon of the invention is greater than about 7 to greaterthan about 8, depending on the polymeric material used. Preferably, theblow up ratio is greater than 7 for a balloon formed of Pellethane 2363.For a balloon formed of Bionate polycarbonate polyurethane, the blow upratio is greater than about 6, preferably greater than about 7, and forimproved balloon fatigue resistance, most preferably 7.6 to about 8.

In one presently preferred embodiment, the noncompliant balloon isformed of a polycarbonate polyurethane such as Bionate® having anelongation at break of at least about 250%, with a compliance of notgreater than about 0.02 mm/atm, and preferably about 0.012 to about0.016 mm/atm over the working pressure range of the balloon. A presentlypreferred Bionate® polycarbonate polyurethane comprises the product ofthe reaction of poly(1,6-hexyl 1,2-ethylcarbonate) diol and4,4′-methylene bisphyenyl diisocyanate (MDI), and a chain extender suchas 1,4-butane diol. Preferably, the noncompliant balloon comprisingBionate® polycarbonate polyurethane is formed from balloon tubingannealed at about 50° C. to about 60° C., and preferably about 50° C. toabout 55° C., for about 16 to about 24 hours. Preferably, the blow upratio is about 7.4 to about 7.8. Other polycarbonate polyurethanesincluding aliphatic diisocyanate based polyurethanes such as Carbothane®have been found to be not preferred in making the noncompliant balloonof the invention, due at least to the low rupture pressure and highcompliance of the balloons as compared to balloons formed from Bionate®.The rupture pressure of the balloon is at least about 18 atm, andpreferably greater than about 18 atm.

EXAMPLE 4

A radially and axially noncompliant balloon was formed of apolycarbonate polyurethane. The polycarbonate polyurethane was Bionate®grade 75D, available from PTG, having an aromatic isocyanate hardsegment such as 4,4′-methylene bis(phenyl isocyanate) (MDI), and apolycarbonate diol soft segment such as poly(1,6-hexyl carbonate) diol(PHCD), and a butanediol chain extender. The Bionate® polyurethane isprepared by reacting the polycarbonate diol which gives rise to the softsegments in the polyurethane with an aromatic isocyanate, and reactingthe resulting prepolymer with the chain extender. The Shore Durometerhardness of the Bionate® is preferably about 65D or higher, and mostpreferably about 75D or higher. The molecular weight is about 100,000 toabout 500,000 Dalton, preferably about 175,000 to about 300,000 Dalton.Bionate® grade 75D having a Shore Durometer hardness of about 75D has aflexural modulus of 307,000 psi, an ultimate tensile strength of about7000 to about 9,100 psi, and an ultimate elongation of about 255% toabout 320%. The Bionate® grade 75D was used to extrude balloon tubinghaving an outer diameter of about 0.031 inch to about 0.034 inch and aninner diameter of about 0.015 inch to about 0.018 inch. The extrudedtubing is preferably not crosslinked. The balloon tubing was annealed at55° C. for 16 hours. After annealing the balloon tubing was expanded ina mold and heat set in the mold as outlined in Example 2, except theblow up ratio of the balloon was 7.6. The resulting balloon had an outerdiameter of 3.0 mm, a working length of 20 mm, and a dual wall thicknessof about 1.5 to about 1.8 mils (0.038 to 0.045 mm). The balloon had aradial compliance of about 0.015 mm/atm from 7 to 22 atm (and about0.016 mm/atm after e-beam sterilization), and about 0.011 mm/atm fromabout 20 atm to about 27 atm. The balloon had an axial growth of 0.75 mmfrom about 9 to 18 atm. The axial growth was about 4% of the original 20mm working length of the balloon, from 9 to 18 atm. The working pressurerange is about 7 to about 18 psi, the mean rupture pressure was about 27atm, and the fatigue at 18 atm was about 95% reliability. A similarballoon prepared by annealing the balloon tubing at 40° C. for 16 hourswhile otherwise using the same procedure outlined above had axial growthof 7.5% to 10%.

It will be apparent from the foregoing that, while particular forms ofthe invention have been illustrated and described, various modificationscan be made without departing from the spirit and scope of theinvention. For example, while the balloon catheter illustrated in FIGS.1 and 7 has inner and outer tubular members with independent lumens, asingle tubular membered shaft having two lumens therein may also beused. Although individual features of embodiments of the invention maybe described or shown in some of the drawings and not in others, thoseskilled in the art will recognize that individual features of oneembodiment of the invention can be combined with any or all the featuresof another embodiment. Other modifications may be made without departingfrom the scope of the invention.

1. A method of making a radially and axially noncompliant balloon for acatheter, comprising a) first extruding a tubular product formed atleast in part of a block copolymer, having a first outer diameter and afirst inner diameter; b) then, prior to any expansion, annealing thetubular product at not less than about 50° C. c) then heating thetubular product at a first elevated temperature, and radially expandingthe tubular product to a second outer diameter; d) then heating theexpanded tubular product at a second elevated temperature not less thanthe first elevated temperature; and e) then cooling the expanded tubularproduct to form the noncompliant balloon.
 2. The method of claim 1wherein the extruded tubular product is annealed for about 16 to about24 hours.
 3. The method of claim 1 wherein the extruded tubular productis annealed at about 55° C.
 4. The method of claim 3 wherein theextruded tubular product is annealed for about 16 hours.
 5. The methodof claim 1 wherein the block copolymer is a polyurethane blockcopolymer, and the tubular product is radially expanded to a blow upratio of greater than about 6 in c), wherein the blow up ratio is theratio of the second outer diameter of the expanded tubular product tothe first inner diameter of the extruded tubular product.
 6. The methodof claim 5 wherein the polyurethane block copolymer is a polycarbonatepolyurethane block copolymer comprising the product of the reaction ofpoly(1,6-hexyl 1,2-ethylcarbonate) diol and 4,4′-methylene bisphyenyldiisocyanate (MDI) and a chain extender, and the noncompliant balloonhas a rupture pressure of at least about 18 atmospheres, and the tubularproduct is radially expanded to a blow up ratio of about 7.4 to about7.8 in c).